[The hollow prosthesis. Reflections on cementless hip endoprosthesis anchorage]

Hollow prostheses appear to represent a promising approach for the durable fixation of cementless hip-joint endoprostheses. The goal of the planned development is the design-engineering, quality-assured production and clinical testing of hollow prostheses displaying largest possible interior space and optimized wall thickness. With hollow prostheses the possibility exists for the first time of filling both the interior space of the prosthesis and cavities between the prosthesis bearing and the prosthesis with spongiosa. Theoretical considerations indicate that this should result in early and durable secondary stability. First results from animal experiments show that the canine femora operated on display a stress distribution closely approximating the natural stress distribution in the bone and exhibit the expected ingrowth of spongiosa into the interior space of the hollow prosthesis. The choice of suitable materials and particularly of wall thickness and cross-sectional shape has a decisive bearing on the elastic behaviour of the prosthesis. Compared with a solid prosthesis of the same geometry, a hollow prosthesis exhibits reduced flexural rigidity and hence higher elasticity. The dynamic tests performed on hollow prostheses in line with DIN 58,840 have shown that--given careful design and manufacture as well as effective quality-assurance measures--fatigue failure is not to be expected in the case of hollow prostheses.